MDL-38923 theme_bootstrapbase: tidied up dock implementation

Also:
* Changed to a CSS based compacting solution
* Converted dock colours to variables
* RTL fixes for the dock

theme/bootstrapbase/javascript/dock.js

@@ -0,0 +1,10 @@
+/**
+ * Customise the dock for this theme.
+ */
+function customise_dock_for_theme() {
+    // Add the "block" class to docked blocks.
+    // This prevents having to restyle all docked blocks and simply use standard block styling.
+    M.core_dock.on('dock:panelgenerated', function(){
+        Y.all('.dockeditempanel_content').addClass('block');
+    });
+}